Process for producing catalyst for methacrylic acid production, catalyst for methacrylic acid production, and process for producing methacrylic acid

ABSTRACT

A method for producing a catalyst containing given atoms in a given atomic proportion for use in producing methacrylic acid through gas-phase catalytic oxidation of methacrolein with molecular oxygen comprising the steps of: (i) preparing a solution or slurry containing at least molybdenum, phosphorus, and vanadium (liquid I); (ii) preparing a solution or slurry containing ammonium radical (liquid II); (iii) preparing a mixture of the liquid I and the liquid II by introducing one liquid (liquid PR) of the liquid I and the liquid II into a tank (tank A) and pouring the other liquid (liquid LA) on a continuous region in the surface of the liquid PR, the continuous region occupying 0.01 to 10% of the whole area of the surface of the liquid PR; and (iv) drying and calcining the resultant solution or slurry containing a catalyst precursor comprising all the catalyst constituents.

TECHNICAL FIELD

The present invention relates to a method for producing a catalyst foruse in producing methacrylic acid (hereinafter, in some cases expressedas methacrylic acid production catalyst) through gas-phase catalyticoxidation of methacrolein with molecular oxygen, a catalyst forproducing methacrylic acid, and a method for producing methacrylic acid.

BACKGROUND ART

In Patent document 1, a method for preparing a catalyst is disclosed,wherein a homogeneous solution containing at least one element selectedfrom molybdenum, vanadium, phosphorous, antimony, copper and the like, ahomogeneous solution containing at least one element selected frompotassium, rubidium, cesium and thallium, a homogeneous solutioncontaining at least one element selected from tungsten, beryllium,magnesium and the like, and ammonia if necessary are mixed and theresultant product is dried to obtain the catalyst.

Further, in Patent document 2, a method for producing a catalyst for usein producing methacrylic acid is disclosed, wherein the following stepis included in which a solution or slurry containing at leastmolybdenum, phosphorous and vanadium and a solution or slurry containingammonium compound are mixed and to the resultant solution or slurry asolution or slurry containing potassium and the like is added.Especially, an embodiment is disclosed in which ammonia water is droppedin a solution containing molybdenum, phosphorus and vanadium to mix bothsolutions.

Patent document 1: Japanese Patent Application, First Publication No.Hei 5-31368

Patent document 2: Japanese Patent Application, First Publication No.2000-296336

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, the catalysts produced by using the methods disclosed in thesepatent documents didn't always realize a sufficient yield of methacrylicacid and, and hence an industrial catalyst with a superior performancehas been desired.

The objects of the present invention are to provide a catalyst forproducing methacrylic acid with a high yield, a method for producing thecatalyst and a method for producing methacrylic acid by using thecatalyst.

Means for Solving Problem

A method for producing methacrylic acid production catalyst of thepresent invention, which has solved the aforementioned problem, is

a method for producing a catalyst having a composition represented bythe following formula (1) for use in producing methacrylic acid throughgas-phase catalytic oxidation of methacrolein with molecular oxygen,comprising the steps of:

(i) preparing a solution or slurry containing at least molybdenum,phosphorus, and vanadium (liquid I);

(ii) preparing a solution or slurry containing ammonium radical (liquidII);

(iii) preparing a mixture of the liquid I and the liquid II byintroducing one liquid (liquid PR) of the liquid I and the liquid IIinto a tank (tank A) and pouring the other liquid (liquid LA) on acontinuous region in the surface of the liquid PR, the continuous regionoccupying 0.01 to 10% of the whole area of the surface of the liquid PR;and

(iv) drying and calcining the resultant solution or slurry containing acatalyst precursor comprising all the aforementioned catalystconstituents.P_(a)Mo_(b)V_(c)Cu_(d)X_(e)Y_(f)Z_(g)O_(h)   (1)

In the aforementioned formula (1), P, Mo, V, Cu and O representphosphorous, molybdenum, vanadium, copper and oxygen, respectively; Xrepresents at least one element selected from the group consisting ofantimony, bismuth, arsenic, germanium, zirconium, tellurium, silver,selenium, silicon, tungsten and boron; Y represents at least one elementselected from the group consisting of iron, zinc, chromium, magnesium,tantalum, cobalt, manganese, barium, gallium, cerium and lanthanum; Zrepresents at least one element selected from the group consisting ofpotassium, rubidium and cesium; and in the formula (1), subscripts a, b,c, d, e, f, g and h represent an atomic ratio of each element,respectively; when b is 12, a is in the range of from 0.5 to 3, c is inthe range of from 0.01 to 3, d is in the range of from 0.01 to 2, e isin the range of from 0 to 3, f is in the range of from 0 to 3, g is inthe range of from 0.01 to 3 and h represents the atomic ratio of oxygennecessary for fulfilling the requirement of the valence of each elementabove.

Further, the method for producing methacrylic acid production catalystof the present invention is characterized in that the aforementionedliquid LA is poured while stirring the liquid PR introduced into theaforementioned tank A with a stirring power of 0.01 to 3.5 kW/m³.

Further, the method for producing methacrylic acid production catalystof the present invention is characterized in that the aforementionedliquid LA is poured from the height of 0.05 to 2 m above the surface ofthe liquid PR introduced into the aforementioned tank A.

Further, the present invention in which the aforementioned problem hasbeen solved resides in the catalyst produced according to theaforementioned method of the present invention.

Further, the present invention in which the aforementioned problem hasbeen solved also resides in a method for producing methacrylic acidthrough gas-phase catalytic oxidation of methacrolein with molecularoxygen in the presence of methacrylic acid production catalyst of thepresent invention.

EFFECT OF THE INVENTION

According to the present invention, it is possible to provide a methodfor producing a catalyst for use in producing methacrylic acid throughgas-phase catalytic oxidation of methacrolein with molecular oxygen, acatalyst with a high yield of methacrylic acid and a method forproducing methacrylic acid by which methacrylic acid can be produced ina high yield.

BEST MODE FOR CARRYING OUT THE INVENTION

The methacrylic acid production catalyst, which can be produced by themethod of the present invention, is used when methacrylic acid isproduced through gas-phase catalytic oxidation of methacrolein withmolecular oxygen and has a composition represented by the followingformula (1).P_(a)Mo_(b)V_(c)CU_(d)X_(e)Y_(f)Z_(g)O_(h)   (1)

In the formula (1), P, Mo, V, Cu and O represent phosphorous,molybdenum, vanadium, copper and oxygen, respectively; X represents atleast one element selected from the group consisting of antimony,bismuth, arsenic, germanium, zirconium, tellurium, silver, selenium,silicon, tungsten and boron; Y represents at least one element selectedfrom the group consisting of iron, zinc, chromium, magnesium, tantalum,cobalt, manganese, barium, gallium, cerium and lanthanum; Z representsat least one element selected from the group consisting of potassium,rubidium and cesium; and subscripts a, b, c, d, e, f, g and h representan atomic ratio of each element, respectively; when b is 12, a is in therange of from 0.5 to 3, c is in the range of from 0.01 to 3, d is in therange of from 0.01 to 2, e is in the range of from 0 to 3, f is in therange of from 0 to 3, g is in the range of from 0.01 to 3 and hrepresents the atomic ratio of oxygen necessary for fulfilling therequirement of the valence of each element above.

The method for producing methacrylic acid production catalyst of thepresent invention comprises the steps of:

(i) preparing a solution or slurry containing at least molybdenum,phosphorus, and vanadium (liquid I);

(ii) preparing a solution or slurry containing ammonium radical (liquidII);

(iii) preparing a mixture of the liquid I and the liquid II byintroducing one liquid (in some cases expressed as liquid PR) of theliquid I and the liquid II into a tank (in some cases expressed as tankA) and pouring the other liquid (in some cases expressed as liquid LA)on a continuous region in the surface of the liquid PR, the continuousregion occupying 0.01 to 10% of the whole area of the surface of theliquid PR; and

(iv) drying the resultant solution or slurry containing a catalystprecursor comprising all the aforementioned catalyst constituents andcalcining the resultant dried catalyst precursor (in some cases “dryingthe resultant solution . . . catalyst constituents and calcining theresultant dried catalyst precursor” is expressed as “drying andcalcining the resultant dried catalyst precursor”).

The ammonium radical in the present invention represents ammonia (NH₃)which can be changed into ammonium (NH₄ ⁺) or ammonium which is includedin ammonium compounds such as ammonium salts.

In the present invention, a tank to be used for preparing the liquid Iand the liquid II and the tank A to be used for mixing both liquids arenot particularly limited and a conventionally known tank can be used,however, a vessel type reactor can be preferably used. Moreover, thetank may be equipped with a stirrer, a baffle board and a jacket or acoil for heat exchanging. The stirrer may be equipped with a publiclyknown mixing blade such as a paddle blade, a propeller blade, a turbineblade, a flat blade, a bent blade or the like in one stage or in two ormore stages in the vertical direction of the stirrer. The stirrer may beequipped with the same type or different types of blades. Further, astirrer which is equipped with blade that is called large blade such asscrew anchor or “MAXBLEND” (registered trade name, manufactured bySumitomo Heavy Industries, Ltd.) can be used.

Hereinafter, a preparing method of the liquid I and the liquid II and amixing method of both liquids are described in detail.

<Preparing Method of the Liquid I>

The liquid I is prepared by dissolving or suspending raw materials suchas compounds of at least molybdenum, phosphorus and vanadium in thesolvent. The liquid I may contain compounds of copper, theaforementioned element X, the aforementioned element Y, theaforementioned element Z, and compounds containing ammonium radical aswell as molybdenum, phosphorus and vanadium.

The amount of ammonium radical contained in the liquid I is notparticularly limited, it is preferably 0 to 1.5 mols per 12 mols ofmolybdenum, more preferably 0 to 1.0 mol. When the amount of ammoniumradical is set in this range, a catalyst with a high yield ofmethacrylic acid can be obtained. The amount of ammonium radicalcontained in the liquid I can be adjusted by the used amount ofcompounds containing the ammonium radical or ammonia.

As a raw material to be used in preparing the liquid I, oxides,nitrates, carbonates, ammonium salts and the like of each aforementionedelement can be exemplified. The raw material can be properly selectedamong these compounds and used in the preparation of the liquid I.

For example, as a compound of molybdenum, a compound which doesn'tcontain ammonium such as molybdenum trioxide, molybdic acid or the likeis preferable, however, ammonium molybdates such as ammoniumparamolybdate, ammonium dimolybdate, ammonium tetramolybdate or the likecan be used if a small amount of them is used. As a compound ofphosphorus, orthophosphoric acid, phosphorus pentoxide, ammoniumphosphate or the like can be used. As a compound of vanadium, vanadiumpentoxide, ammonium metavanadate or the like can be used. Further, as acompound of phosphorus, molybdenum and vanadium, heteropolyacid such asphosphomolybdic acid, phosphovanadomolybdic acid, ammoniumphosphomolybdate or the like can be used.

For each element, these compounds may be used alone or in combination oftwo or more kinds.

As a solvent which can be used in preparing the liquid I, for example,water, ethyl alcohol and acetone can be exemplified, however, water ispreferably used. The amount of the solvent in the liquid I is notparticularly limited, however, usually the content ratio (mass ratio) ofthe molybdenum compound to the solvent contained in the liquid I ispreferably 1:0.1 to 1:100, more preferably 1:0.5 to 1:50. When theamount of the solvent is set in this range, a catalyst with a high yieldof methacrylic acid can be obtained.

The liquid I can be prepared by mixing the aforementioned compound to beused as a raw material and the solvent, and stirring the resultantmixture at an ordinary temperature to dissolve or suspend the compoundto make a solution or slurry. Generally, the stirring is preferablyperformed while heating. Usually, the heating temperature is preferably80° C. or more, more preferably 90° C. or more. Further, the heatingtemperature is, usually, preferably 150° C. or less, more preferably130° C. or less. When the heating temperature is set in this range, acatalyst with a high activity can be obtained. The heating time is,usually, preferably 0.5 hour or more, more preferably 1 hour or more.The heating time is, usually, preferably 24 hours or less, morepreferably 12 hours or less. When the heating time is set in this range,the aforementioned compound can be easily dissolved or suspended,thereby the reaction among the raw materials can be sufficientlypromoted.

Further, a compound of the aforementioned element Z is preferably mixedwith the solvent and dissolved or suspended to prepare a solution orslurry (in some cases expressed as liquid III), and the resultantsolution or slurry is preferably added to a solution or slurrycontaining molybdenum, phosphorus and vanadium. At this time, thetemperature of the solution or slurry is preferably 80° C. or less, morepreferably 30 to 70° C. As the element Z, cesium is preferable becausean especially superior effect can be obtained. Foe example, as a cesiumcompound to be used as a raw material in the preparation of the liquidI, cesium nitrate, cesium carbonate, cesium hydroxide or the like can beused. As the cesium compound, these compounds may be used alone or incombination of two or more kinds.

<Preparing Method of the Liquid II>

The liquid II can be prepared by dissolving or suspending compoundscontaining ammonium radical in the solvent.

The liquid II may contain compounds of phosphorus, molybdenum, vanadium,copper, the aforementioned element X, the aforementioned element Y, andthe aforementioned element Z as well as compounds containing ammoniumradical, however, it is preferable that these compounds aresubstantially not contained.

The amount of the ammonium radical contained in the liquid II is notparticularly limited, however, it is preferably 6 mols or more per 12mols of molybdenum contained in the liquid I, and more preferably 7 molsor more. Further, the amount of the ammonium radical contained in theliquid II is preferably 17 mols or less per 12 mols of molybdenumcontained in the liquid I, and more preferably 15 mols or less. When theamount of the ammonium radical is set in this range, a catalyst with ahigh yield of methacrylic acid can be obtained.

An ammonium radical containing compound which can be used in preparingthe liquid II is ammonia or ammonium salt. Specifically, ammonia(ammonia water), ammonium carbonate, ammonium hydrogencarbonate,ammonium nitrate or the like can be exemplified as the compound. As theammonium radical-containing compound, these compounds may be used aloneor in combination of two or more kinds.

As a solvent which can be used in preparing the liquid II, for example,water, ethyl alcohol and acetone can be exemplified, however, usually,water is preferably used. The amount of the solvent in the liquid II isnot particularly limited, however, usually, the content ratio (massratio) of the ammonium radical-containing compound to the solventcontained in the liquid II is preferably 1:0.1 to 1:100, more preferably1:0.5 to 1:50. When the amount of the solvent is set in this range, acatalyst with a high yield of methacrylic acid can be obtained.

The liquid II can be prepared by adding the ammonium radical-containingcompound to the solvent, stirring the resultant mixture at an ordinarytemperature to dissolve or suspend the compound to make a solution orslurry. The liquid can be prepared by heating the resultant mixture upto around 80° C. when it is necessary. However, in case that ammoniawater itself is used as the ammonium radical-containing compound, thesepreparing steps are not always necessary, because water which serves assolvent is already included.

<Mixing the Liquid I and the Liquid II>

In the present invention, the liquid I and the liquid II are mixed byintroducing one liquid (liquid PR) of the liquid I and the liquid IIinto a tank (tank A) and pouring the other liquid (liquid LA) into thetank A. In case that the liquid I or the liquid II is prepared in thetank A, the resultant liquid itself serves as the liquid PR introducedinto the tank A. It is important that the liquid LA is poured on acontinuous region in the surface of the liquid PR introduced into thetank A, the continuous region occupying 0.01 to 10%, more preferably0.05 to 5% of the whole area of the surface of the liquid PR.

By pouring the liquid LA into the liquid PR and mixing both liquids inthis manner a catalyst with a high yield of methacrylic acid can beobtained. It is supposed that the local pH distribution in the vicinityof the mixed portion of the liquid I and the liquid II favorably acts toform an effective crystal structure for the oxidation of methacroleinand makes it possible to obtain a catalyst with a high yield ofmethacrylic acid.

When the liquid LA is poured into the tank A, the liquid PR introducedinto the tank A is stirred with a stirring power of preferably 0.01 to3.5 kW/m³, more preferably 0.05 to 3 kW/m³. By stirring the liquid PR inthe range of the aforementioned stirring power, it is supposed that aneffective crystal structure for the oxidation of methacrolein is formedso that the yield of methacrylic acid of the catalyst thus obtained isimproved.

Further, when the liquid LA is poured into the tank A, the liquid LA ispoured from the height of preferably 0.05 to 2 m, more preferably 0.1 to1.5 m above the surface of the liquid PR introduced into the tank A.When the liquid LA is poured from the height of 0.05 m or more above thesurface of the liquid PR, the liquid PR does not contact with thepouring port of the liquid LA even in the case that the liquid PR isstirred, and when the liquid LA is poured from the height of 1.5 m orless above the surface of the liquid PR, the liquid LA is not dispersedor does not contact with the wall of the tank A. Consequently, it issupposed that an effective crystal structure for the oxidation ofmethacrolein is formed so that the yield of methacrylic acid of thecatalyst thus obtained is improved.

In the present invention, a method of pouring the liquid LA into thetank A is not particularly limited, however, a method of pouring theliquid LA by free fall from an upper part or a side part of the tank Athrough a pipe connected to a tank containing the liquid LA, or a methodof quantitatively sending the liquid with pump and the like can beexemplified.

Number of the pouring port for pouring the liquid LA into the tank A isnot particularly limited, and either one or a plurality of the pouringports may be used as far as the liquid LA is poured on a continuousregion in the surface of the liquid I and the liquid II introduced intothe tank A. The number of the pouring port is preferably one undernormal conditions.

In the present invention, it is possible to serve the aforementionedliquid I as the liquid PR and to serve the aforementioned liquid II asthe liquid LA, or to serve the aforementioned liquid II as the liquid PRand to serve the aforementioned liquid I as the liquid LA. Further, theliquid LA can be divided into portions and poured separately in two ormore times. The temperatures of the liquid LA and the liquid PR at thetime when the liquid LA is poured are not particularly limited, and theyare preferably 100° C. or less, more preferably 80° C. or less, andpreferably the room temperature or more under normal conditions.

The liquid LA can be poured while stirring it.

When it is preferable, first, the mixture of the liquid I and the liquidII may be prepared without including the element Z according to theaforementioned method, and then the solution or slurry (the liquid III)containing the compound of the element Z may be added.

A introducing method of the liquid III is not particularly limited, and,for example, a method of introducing the liquid III to the mixture ofthe liquid I and the liquid II, a method of introducing the mixture ofthe liquid I and the liquid II to the liquid III, or a method ofintroducing the liquid III and the mixture of the liquid I and theliquid II at the same time can be adopted.

In the preparation of the solution or slurry containing a catalystprecursor comprising all the catalyst constituents, the liquid I and theliquid II (and further the liquid III when it is preferable) may bemixed under normal room temperature or under heating. The mixingtemperature is preferably 100° C. or less, more preferably 80° C. orless, and preferably the room temperature or more under normalconditions. By mixing the liquid I and the liquid II (and further theliquid III when it is preferable) under such range of the liquidtemperature and preparing the solution or slurry containing the catalystprecursor, a catalyst with a high activity is obtained. Usually, themixing is performed while stirring. Further, the mixing time is notparticularly limited, and determined properly.

<Drying/Calcining>

After the solution or slurry containing a catalyst precursor comprisingall the catalyst constituents is obtained in this manner, the solutionor slurry is dried and a dried catalyst precursor is obtained.

The drying method of the solution or slurry containing a catalystprecursor is not particularly limited, and a variety of methods can beused. For example, evaporation drying method, spray drying method, drumdrying method, airborne drying method or the like can be used. Type ofthe dryer to be used in the drying, drying temperature, drying time andthe like are not particularly limited, and different types of driedcatalyst precursors for different purposes can be obtained by properlychanging the drying condition.

The dried catalyst precursor thus obtained is ground when it ispreferable and calcined to prepare a catalyst. The dried catalystprecursor may be molded in advance and calcined or can be calcinedwithout molding it. Usually, it is preferable to make a molded form andcalcine it to prepare a catalyst.

The molding method is not particularly limited, and a variety of dry orwet methods publicly known can be applied. A molding method in whichsilica and the like are used as a carrier can also be applied. Usually,a method in which carrier is not used is preferable. As a specificmolding method, tablet molding, press molding, extrusion molding,granulation molding and the like are exemplified. The shape of themolded form is not particularly limited, and a cylindrical shape, a ringshape, a spherical shape and the like can be selected at request.

At the time of molding, a publicly known additive such as graphite, talcand the like may be added with a small quantity.

The dried catalyst precursor or its molded form thus obtained iscalcined to prepare a catalyst for use in producing methacrylic acid.The calcining method and the calcining condition are not particularlylimited, and a publicly known calcining method and a publicly knowncalcining condition can be applied. The optimum calcining condition isdifferent depending on the catalyst raw material to be used, thecatalyst composition, the catalyst preparing method and the like, and anormal condition of calcining under the flow of an oxygen containing-gassuch as air or an inert gas is as follows: the calcining temperature is200 to 500° C., preferably 300 to 450° C.; the calcining time is 0.5hour or more, preferably 1 to 40 hours. Here, the inert gas means a gaswhich doesn't lower the reaction activity of the catalyst. As such agas, specifically, nitrogen, carbon dioxide, helium, argon and the likecan be exemplified.

<Method for Producing Methacrylic Acid>

Hereinafter, a method for producing methacrylic acid of the presentinvention is explained.

A method for producing methacrylic acid of the present invention is themethod for producing methacrylic acid through gas-phase catalyticoxidation of methacrolein with molecular oxygen in the presence of thecatalyst of the present invention obtained as mentioned above.

In the aforementioned method for producing methacrylic acid of thepresent invention, a raw gas including methacrolein and molecular oxygenis subjected to contact with a catalyst. The concentration ofmethacrolein in the raw gas can be changed in a wide range. Usually, theconcentration of methacrolein is 1 to 20% by volume and preferably 3 to10% by volume in particular. A small quantity of impurities such as lowsaturated aldehyde and the like may be contained in the raw gas.However, it is preferable to keep the quantity as small as possible.

As a molecular oxygen source, air is used from economical reason. A pureoxygen enriched air and the like can be used when it is preferable. Theconcentration of molecular oxygen in the raw gas is usually 0.4 to 4mols, and preferably 0.5 to 3 mols per 1 mol of methacrolein inparticular. The raw gas may be diluted by adding an inert gas such asnitrogen, carbon dioxide or the like. Further, the raw gas may be addedwith water vapor. The concentration of water vapor in the raw gas isusually 0.1 to 50% by volume, and preferably 1 to 40% by volume inparticular. When the reaction is carried out in the presence of watervapor, methacrylic acid can be obtained with a higher yield.

The gas-phase catalytic oxidation of methacrolein is usually carried outin a fixed-bed. The number of the catalyst layer may be one, or two ormore. The catalyst may be supported on a carrier or mixed with the otheradditives. The reaction pressure is preferably from ordinary pressure toseveral atmospheric pressures. The reaction temperature is usuallyselected in the range of from 230 to 450° C., and is preferably 250 to400° C. in particular. The flow rate of the raw gas is not particularlylimited, and usually the flow rate expressed in terms of contact time is1.5 to 15 seconds, preferably 2 to 5 seconds.

The mechanism related to the improvement of the catalyst performance inthe method for producing methacrylic acid of the present invention isnot fully elucidated, however, as mentioned above, it is supposed thatthe local pH distribution in the vicinity of the mixed portion of theliquid I and the liquid II at the time of pouring the liquid LA into theliquid PR favorably acts to form an effective crystal structure for theoxidation of methacrolein and makes it possible to form a crystalstructure with a high yield of methacrylic acid.

EXAMPLES

Hereinafter, the present invention will be entered into details withreference to the following examples and comparative examples. However,the present invention is not limited to these examples.

The catalyst composition was determined from the charged amount of thecatalyst raw materials. Further, the analysis of the raw gas and thereaction products in the production of methacrylic acid was carried outusing gas chromatography. Based on the analytical results obtained, theconversion of methacrolein (may be expressed as MAL conversion), theselectivity to produced methacrylic acid (may be expressed as MAAselectivity) and the single current yield of methacrylic acid (may beexpressed as MAA yield) were determined by the following formulae,respectively.The conversion of methacrolein (%)=(B/A)×100The selectivity to methacrylic acid (%)=(C/B)×100The single current yield of methacrylic acid (%)=(C/A)×100

In these formulae, A is a number of mol(s) of the supplied methacrolein,B is a number of mol(s) of the reacted methacrolein and C is a number ofmol(s) of the produced methacrylic acid.

Further, the percentage of the area (S₁) of the liquid surface region onwhich the liquid LA was poured to the whole area of the surface of theliquid PR (may be expressed as Sp), was determined by the followingformula. The whole area of the surface of the liquid PR (Sp) is ahorizontal cross section inside the tank A at the height of the surfaceof the liquid PR, and the area (S₁) of the liquid surface region onwhich the liquid LA was poured was a horizontal cross section of thepoured liquid LA at the height of the surface of the liquid PR. Further,in the examples, S₁ was determined as the aperture area of the pouringport because the liquid LA was poured in the liquid PR with the samesize of the aperture area of the pouring port.

The percentage of the area of the surface region on which the liquid LAwas poured to the whole area of the surface of the liquid PR(%)=(S₁/Sp)×100

Example 1

To a vessel type reactor (tank A) with a diameter of 340 mm and aninternal volume of 30 L, 10 kg of pure water having a room temperaturewas introduced and a solution obtained by dissolving 5000 g ofmolybdenum trioxide, 366.5 g of 85 mass % phosphoric acid, 202.8 g ofammonium methavanadate, 69.8 g of copper nitrate in 610 g of pure waterand a solution obtained by dissolving 58.4 g of ferric nitrate in 250 gof pure water were added while stirring with a one-stage paddle bladeand the resultant mixture was heated to 98° C. and kept at 98° C. for 5hours while stirring. The resultant mixture was cooled to 50° C. and asolution obtained by dissolving 732.3 g of cesium in 1250 g of purewater was added to make a mixed liquid which is served as liquid I.

On the other hand, 1988 g of 25 mass % ammonia water was introduced to areactor (tank B) with an internal volume of 2 L at room temperature tomake liquid II.

The liquid I which was kept at 50° C. in the tank A and served as liquidPR was stirred with a stirring power of 0.2 kW/m³ and the liquid IIserved as liquid LA was poured in the liquid PR from a pouring port of20 mm in diameter at the height of 0.3 m above the surface of the liquidPR to obtain a slurry containing a catalyst precursor. The liquidsurface region on which the liquid LA was poured was a continuous regionwith an almost circular shape having a diameter of around 20 mm and thepercentage of the area of the aforementioned liquid surface region onwhich the liquid LA was poured to the whole area of the surface of theliquid PR was 0.4%.

The resultant slurry containing the catalyst precursor was heated to110° C. and evaporated and dried while stirring. The resultant solidmaterial was dried at 130° C. for 16 hours and dried material wasobtained. The resultant dried material was press molded and calcined at380° C. for 12 hours under airflow to obtain a catalyst. The compositionof the catalyst thus obtained was P_(1.1) Mo₁₂ V_(0.6) Cu_(0.1)Fe_(0.05) Cs_(1.3).

<Reaction for Synthesizing Methacrylic Acid>

The resultant catalyst was packed in a reaction tube and a mixed gascontaining 5% by volume of methacrolein, 10% by volume of oxygen, 30% byvolume of water vapor and 55% by volume of nitrogen was flowed and thereaction was carried out under an ordinary pressure, at a reactiontemperature of 290° C., with a contact time of 3.6 seconds. The resultsare shown in Table 1.

Example 2

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 1 except that the liquid LA (the liquid II)was poured in the liquid PR (the liquid I) in the tank A from a pouringport of 40 mm in diameter. The results are shown in Table 1.

Example 3

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 1 except that the liquid LA (the liquid II)was poured in the liquid PR (the liquid I) in the tank A from a pouringport of 100 mm in diameter. The results are shown in Table 1.

Example 4

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 1 except that the liquid PR was stirred with astirring power of 4.0 kW/m³. The results are shown in Table 1.

Comparative Example 1

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 1 except that the liquid LA (the liquid II)was poured in the liquid PR (the liquid I) in the tank A from a pouringport of 150 mm in diameter. The results are shown in Table 1.

Comparative Example 2

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 1 except that the liquid LA was poured in theliquid PR (the liquid I) in the tank A from a pouring port of 2 mm indiameter. The results are shown in Table 1.

Comparative Example 3

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 1 except that the liquid LA (the liquid II)was poured in the liquid PR (the liquid I) in the tank A from 10 pouringports of 20 mm in diameter arranged in a ring shaped pipeline providedalong the inner wall of the tank A to 10 different regions of thesurface. The results are shown in Table 1.

Example 5

To a vessel type reactor (tank A) with a diameter of 650 mm and aninternal volume of 250 L, 100 kg of pure water was introduced at roomtemperature and 50 kg of molybdenum trioxide, 2.67 kg of 85 mass %phosphoric acid, 1.84 kg of vanadium pentoxide, and 5.48 kg of 60 mass %arsenic acid aqueous solution were added while stirring with a two stagepaddle blade and the resultant mixture was heated to 98° C. and kept at98° C. for 5 hours while stirring. After 5 hours had passed, a solutionobtained by dissolving 1.40 kg of copper nitrate in 6.10 kg of purewater and a solution obtained by dissolving 0.62 kg of zirconium nitratein 3.0 kg of pure water were further added and heated and stirred for 2hours and then cooled to 30° C. to make a mixed liquid which served asliquid I.

To a vessel type reactor (tank B) with an internal volume of 100 L, 18.1kg of 25 mass % ammonia water was introduced at room temperature to makeliquid II.

The liquid PR (the liquid I) which was kept at 30° C. in the tank A wasstirred with a stirring power of 1.1 kW/m³ and the liquid LA (the liquidII) was poured from a pouring port of 100 mm in diameter at the heightof 1.0 m above the liquid surface in the tank A to obtain a mixed liquidof the liquid I and the liquid II. The liquid surface region of theliquid PR (the liquid I) on which the liquid LA was poured was acontinuous region with an almost circular shape having a diameter ofaround 100 mm and the percentage of the area of the aforementionedliquid surface region on which the liquid LA was poured to the wholearea of the surface of the liquid PR was 2.4%.

To the mixed liquid of the liquid I and the liquid II kept at 30° C., asolution obtained by dissolving 6.18 kg of cesium bicarbonate in 15 kgof pure water (the liquid III) was further added to obtain a slurrycontaining a catalyst precursor.

The resultant slurry containing the catalyst precursor was heated to101° C. and evaporated and dried while stirring. The resultant solidmaterial was dried at 130° C. for 16 hours. The resultant dried materialwas pressure molded and calcined at 380° C. for 12 hours under airflow.The composition of the catalyst thus obtained was P_(0.8) Mo₁₂ V_(0.7)Cu_(0.2) As_(0.8) Zr_(0.05) Cs_(1.1).

Using the catalyst, the reaction was carried out in the same manner asin Example 1. The results are shown in Table 1.

Example 6

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 5 except that the liquid LA (the liquid II)was poured in the liquid PR (the liquid I) in the tank A from a pouringport at the height of 2.5 m above the liquid surface of the tank A. Theresults are shown in Table 1.

Comparative Example 4

The preparation of the catalyst and the reaction were carried out in thesame manner as in Example 5 except that the liquid LA (the liquid II)was poured in the liquid PR (the liquid I) in the tank A from 2 pouringports of 50 mm in diameter, each of which was arranged in the diagonaldirection of 180° with respect to the total liquid surface of the tank A(interval of which was 500 mm), to 2 different almost circular regionsof the surface. The results are shown in Table 1. TABLE 1 The percentageof the area of the The shape of liquid the area of surface the liquidregion on surface The height which the region on at which liquid LAwhich the Stirring the liquid MAL MAA was poured liquid LA power LA wasconversion selectivity MAA (%) was poured (kW/m³) poured (m) (%) (%)yield (%) Example 1 0.4 continuous 0.2 0.3 83.1 86.7 72.0 Example 2 1.4continuous 0.2 0.3 82.8 87.0 72.0 Example 3 8.7 continuous 0.2 0.3 80.487.2 70.1 Example 4 0.4 continuous 4.0 0.3 78.8 87.0 68.6 Comparative19.5 continuous 0.2 0.3 76.5 86.3 66.0 Example 1 Comparative 0.001continuous 0.2 0.3 76.0 86.5 65.7 Example 2 Comparative 3.5discontinuous 0.2 0.3 79.6 85.4 68.0 Example 3 Example 5 2.4 continuous1.1 1.0 81.4 88.3 71.9 Example 6 2.4 continuous 1.1 2.5 80.5 87.5 70.4Comparative 1.2 discontinuous 1.1 1.0 79.4 85.8 68.1 Example 4

INDUSTRIAL APPLICABILITY

A method for producing a catalyst for use in producing methacrylic acidand the catalyst produced according to the method of the presentinvention can be suitably used in a method for producing methacrylicacid, including the method for producing methacrylic acid of the presentinvention, through gas-phase catalytic oxidation of methacrolein withmolecular oxygen.

1. A method for producing a catalyst having a composition represented bythe following formula (1) for use in producing methacrylic acid throughgas-phase catalytic oxidation of methacrolein with molecular oxygen,comprising the steps of: (i) preparing a solution or slurry containingat least molybdenum, phosphorus, and vanadium (liquid I); (ii) preparinga solution or slurry containing ammonium radical (liquid II); (iii)preparing a mixture of the liquid I and the liquid II by introducing oneliquid (liquid PR) of the liquid I and the liquid II into a tank (tankA) and pouring the other liquid (liquid LA) on a continuous region inthe surface of the liquid PR, the continuous region occupying 0.01 to10% of the whole area of the surface of the liquid PR; and (iv) dryingand calcining the resultant solution or slurry containing a catalystprecursor comprising all the catalyst constituents,P_(a) Mo_(b) V_(c) Cu_(d) X_(e) Y_(f) Z_(g) O_(h)   (1) wherein P, Mo,V, Cu and O represent phosphorous, molybdenum, vanadium, copper andoxygen, respectively; X represents at least one element selected fromthe group consisting of antimony, bismuth, arsenic, germanium,zirconium, tellurium, silver, selenium, silicon, tungsten and boron; Yrepresents at least one element selected from the group consisting ofiron, zinc, chromium, magnesium, tantalum, cobalt, manganese, barium,gallium, cerium and lanthanum; Z represents at least one elementselected from the group consisting of potassium, rubidium and cesium;and subscripts a, b, c, d, e, f, g and h represent an atomic ratio ofeach element, respectively; when b is 12, a is in the range of from 0.5to 3, c is in the range of from 0.01 to 3, d is in the range of from0.01 to 2, e is in the range of from 0 to 3, f is in the range of from 0to 3, g is in the range of from 0.01 to 3 and h represents the atomicratio of oxygen necessary for fulfilling the requirement of the valenceof each element above.
 2. The method for producing the catalyst for usein producing methacrylic acid according to claim 1, wherein the liquidLA is poured while stirring the liquid PR introduced into the tank Awith a stirring power of 0.01 to 3.5 kW/m³.
 3. The method for producingthe catalyst for use in producing methacrylic acid according to claim 1,wherein the liquid LA is poured from the height of 0.05 to 2 m above thesurface of the liquid PR introduced into the tank A.
 4. A catalystproduced by the method according to claim
 1. 5. A catalyst produced bythe method according to claim
 2. 6. A catalyst produced by the methodaccording to claim
 3. 7. A method for producing methacrylic acid throughgas-phase catalytic oxidation of methacrolein with molecular oxygen inthe presence of the catalyst according to claim
 4. 8. A method forproducing methacrylic acid through gas-phase catalytic oxidation ofmethacrolein with molecular oxygen in the presence of the catalystaccording to claim
 5. 9. A method for producing methacrylic acid throughgas-phase catalytic oxidation of methacrolein with molecular oxygen inthe presence of the catalyst according to claim 6.